There are many areas, including laboratory and production manufacturing in which accurate sensing of a physical variables is necessary for process control and measurement. However, problems have been encountered with prior art sensors when it is necessary for the sensor to be extremely sensitive to a particular variable.
Sensing of a variable magnitude is often performed by mechanically measuring the magnitude of the variable by means of an analog transducer. If the changes in the sensed variable are very small, then the analog transducer must also be extremely sensitive, rendering it susceptible to interference by noise and to changes in other, extraneous variables such as temperature and atmospheric pressure.
In order to overcome some of the problems with noise and interference, various prior art arrangements have been used including differential signal processing arrangements and analog-to-digital conversion (at a location as close as possible to the transducer) and subsequent digital signal processing.
While digitizing a signal has many advantages, it also subjects the measurement process to some noise of its own due to noise in the analog-to-digital conversion process and noise and distortion in the analog transducer.
Accordingly, it is an object of the present invention to provide a sensitive sensor which can directly translate changes in the magnitude of a measured variable into changes in frequency which can be used with conventional digital signal processing circuitry.
It is another object of the present invention to provide a fiber laser sensor which directly converts changes in a monitored variable into changes in the laser output frequency.
It is yet another object of the present invention to provide a sensor which can be designed to selectively monitor one variable while excluding interference from others.
It is still another object of the present invention to provide a sensor which uses a laser oscillator as the sensing element.
It is a further object of the present invention to provide a sensor construction which can be easily fabricated using known techniques.
It is a still further object of the present invention to provide a sensor construction which can be easily adapted to produce both high and low output power.
It is yet another object of the present invention to provide a fiber laser sensor which can be used in a differential mode to further exclude noise and distortion.
It is still another object of the present invention to provide two or more laser sensors in a small, integrated structure with the lasers having differential sensitivity to a plurality of variables so that the frequency outputs developed by the lasers can be used to determine the values of the variables independently.